Thermal printer

ABSTRACT

A thermal printer which may be used to provide a hard copy readout for an electronic device such as a calculator, cash register, computer or the like. The thermal printer includes a printing head having a thermal printing matrix thereon, the printing head being mounted on a carriage which is slidably and pivotally mounted on an elongated cylindrical rod so as to permit the carriage and printhead to be moved linearly along the rod between first and second end positions through intermediate atrest and initial recording positions, and also to permit the carriage and printhead to be pivoted transversely from a printing position with the matrix engaging a stip of thermally sensitive paper, and an inactive position spaced therefrom. The carriage and printhead are moved linearly from position to position in equally spaced incremental steps, as by a stepper motor having a pinion engaging a rack on the carriage. The carriage engages a ramp upon linear movement of the carriage to the at-rest position in the direction toward the first end position thereby pivoting the carriage and printing head to the inactive position, and the carriage and printing head are spring-biased to the printing position between the at-rest position and the second end position. Linear movement of the carriage from the at-rest position to the first end position causes advance of the strip of paper.

United States Patent [191 Herr et a1.

[ Nov. 5, 1974 THERMAL PRINTER [75] Inventors: Robert W. Herr; Edward D. Sigl;

Marion W. Aksamit, all of Fort Wayne, Ind.

I [73] Assignee: Bowmar Instrument Corporation,

Fort Wayne, Ind.

[22] Filed: Feb. 22, 1973 [21] Appl. No.: 334,668

[58] Field of Search 197/1 R, 55, 60, 66, 127 R, 197/133 R, 12,14, 19, 82, 95, 96; 101/93 C; 346/76; 340/324 M; 219/216; 178/42 {56] References Cited UNITED STATES PATENTS 2,900,066 8/1959 Tholstrup 197/32 2,984,328 5/1961 Lambert 197/66 2,997,152 8/1961 Dirks 197/1 R 3,300,017 1/1967 Yazejian et al. 197/1 R 3,429,414 2/1969 Bradbury 197/133 R 3,509,980 5/1970 Loughry et a1 197/1 R 3,578,129 5/1971 Kato et a]. 197/19 3,598,218 8/1971 Gilovich et al 197/1 R 3,643,775 2/1972 Kittel et a]. 197/66 3,710,913 l/l973 Brennen lr. et a1, 346/76 R 3,755,806 8/1973 Bunting. 340/324 R Primary Examiner-Robert E. Pulfrey Assistant Examiner-E. H. Eickholt 57 ABSTRACT A thermal printer which may be used to provide a hard copy readout for an electronic device such as a calculator, cash register, computer or the like. The thermal printer includes a printing head having a thermal printing matrix thereon, the printing head being mounted on a carriage which is slidably and pivotally mounted on an elongated cylindrical rod so as to permit the carriage and printhead to be moved linearly along the rod between first and second end positions through intermediate at-rest and initial recording positions, and also to permit the carriage and printhead to be pivoted transversely from a printing position with the matrix engaging a stip of thermally sensitive paper, and an inactive position spaced therefrom. The carriage and printhead are moved linearly from position to position in equally spacedincremental steps, as by a stepper motor having a pinion engaging a rack on the carriage. The carriage engages a ramp upon linear movement of the carriage to the at-rest position in the direction toward the first end position thereby pivoting the carriage and printing head to the inactive position, and the carriage and printing head are springbiased to the printing position between the at-rest position and the second end position. Linear movement of the carriage from the at-rest position to the first end position causes advance of the strip of paper,

20' Claims, 17 Drawing Figures AT-EEST POSITION FEEDBACK PATENTEI] IIIIV 5 I974 SIIEEIIIIFT PRINTER ADVANCE PULSES PRINTER COMMAND PULSE GENERATOR Fume . FWD

MOTOR CONTROL 26b ENABLE DRIVE CIRCUIT STE PPE IE I MOTOR I CARRIAGE LIMIT SWITCH PAIENTEUxuv 5:974 mm a 7 53,845,850

i //2 HIHIIIIIHHH I ADVANCE.

PAPER I I I PATENTEII 5 I974 MINI? I 2 S X 240 FIG I5 8 23 BCD DATA Z44 246 //0 DATA CALCULATOR |NTERFACE CHAEATER TEERMAL THERMAL ELECTRONICS GENERATOR HEAD AND DRWE- MATRIX CONTROL R l I ADVANCE ENABLE FUNCTION zgz 250 262 20 ME ANI M 254- ig E 3 MECHANISM pRlNTER 256- Tiqmuge DR'VER MECHANISM N AT- REST POSITION FEEDBACK CQNTRQL CARRIAGE LIMIT SWITCH THERMAL PRINTER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to apparatus for electrically recording successive lines of alpha-numeric and symbolic information on a sheet of recording medium for visual display, and more particularly to a thermal printer.

2. Description of the Prior Art It is desirable to provide a hard copy readout for an electronic device such as a calculator, cash register, computer, or the like without the noise associated with a conventional impact printer. Alpha-numeric and symbolic information may be visually recorded or printed on thermally sensitive paper by a solid state thermal printhead containing a matrix or other arrangement of heating elements which upon selective energization form the desired characters. Each heating element may consist of a single crystalline semiconductor body in a mesa shape, each mesa containing a transistor pair. Upon selective energization, the power dissipated by the resistor causes the top surface of the selected mesa to become hot producing a permanent, localized dot on the thermally sensitive paper pressed against it. A five by five or five by seven matrix of heater elements will form a font of all conventional alpha-numeric and symbolic characters. Such thermal printing heads are more fully described in United States Pat. Nos. 3,354,565 and 3,496,333, and in Texas Instruments application report CA-l63, September I971.

Two types of thermal printing apparatus have been provided employing such thermal printing heads. In one such type, as shown for example in US. Pat. Nos. 2,917,996 and 3,453,648, the printing head is stationery and the paper is moved relative thereto. In a second type, as shown for example in US. Pat. Nos. 3,509,980 and 3,638,197, the printing head is mounted on a carriage which is moved relative to the paper by a cable system.

SUMMARY OF THE INVENTION It is desirable to provide thermal printing apparatus of the type in which the printing head is moved relative to the paper. characterized by its simplicity, ease of assembly, and thus relatively low cost.

The invention, in its broaderaspects, provides apparatus for electrically recording successive lines of alpha-numeric and symbolic information on a sheet of recording medium forvisual display including means for holding the sheet to present a recording area upon which a line of information is to be recorded, a recording head having a plurality of recording elements thereon which upon selective energization form alphanumeric and symbolic characters and visually record the same, sequentially, on the recording area, and

means for supporting the recording head with the recording elements facing the recording area. Means are provided for mounting the supporting means for linear movement between first and second spaced end positions through intermediate and initial at-rest recording positions thereby to traverse'the recording head across the recording area, the mounting means also mounting the supporting means for transverse movement between a=recording position with the recording elements engaging the recording area and an inactive position with the recording elements spaced therefrom. Means are provided forlinearly moving the supporting means on the mounting means, and for transversely moving the supporting means on the mounting means to the inactive position in response to linear movement of the supporting means from the initial recording position to the at-rest position in a direction toward the first end position, that means also maintaining the supporting means in its inactive position in all linear positions between the at-rest position and the first end position. Means are further provided for maintaining the supporting means in its recording position in all linear positions between the initial recording position and the second end position.

It is accordingly an object of the invention to provide an improved apparatus for electrically recording successive lines of alpha-numeric information on a sheet of recording medium for visual display.

Another object of the invention is to provide improvedthermal printing apparatus.

A further object of the invention is to provide improved thermal printing apparatus of the type in which a thermal printing head is moved with respect to thermally sensitive paper. I

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS l 9 FIG. 1 is a view in perspective showing the improved thermal printing apparatus of the invention;

FIG. 2 is a top view, partly broken away, of the apparatus of FIG. l showing the printing head at the extreme right-hand position;

FIGS. 3A and 3B are diagrams useful to explaining the operation of the improved thermal printing apparatus of the invention;

, FIG. 4 is a cross-sectional view taken generally along the line 4-4 of FIG. 2 but showing the printing head moved toward the left to its printing position;

FIG. 5 is a fragmentary cross-sectional view taken generally along the line 5-5 of FIG. 2;

FIG. 6 is a fragmentary cross-sectional view taken generally along the line 6-6 of FIG. 2;

FIG. 7 is a cross-sectional view taken generally along the line 77 of FIG. 2;

FIG. 8 is a cross-sectional view taken generally along the line 8-8 of FIG. 2; v

FIG. 9 is a cross-sectional view taken generally along the line 9-9 of FIG. 7;

FIG. 10 is a fragmentary cross-sectional view taken generally along the line 10-10 of FIG. 9; I

FIG. 11 is a fragmentary cross-sectional view taken generally along the line 11-llof FIG. 9;

FIG. 12 is a fragmentary side view of the ratchet part of the paper advancing mechanism as viewed generally along the line 12-12 of FIG. 10;

FIG. 13 is an enlarged view showing the printing side of the printhead;

FIG. 14 is a top view showing the thermal printer of the invention incorporated in an electronic calculator;

FIG. is a block diagram showing an interface and driving system which may be employed with the thermal printing apparatus of the invention; and

FIG. 16 is a block diagram showing'a part of the system of FIG. 15 in greater detail.

DESCRIPTION OF THE PREFERRED EMBODIMENT 'front wall 44 for accommodating the printing mechanism. Top wall 28 has portion 46 projecting forwardly between front edges 42 and having a forwardly and downwardly inclined surface 48 having an extension of slot therein for guiding strip 32 to roller 34 (FIG. 7).

Roller 34 is mounted on shaft 50 supported by brackets 52, 54 which extend forwardly on either side of portion 46 of top wall 28. Brackets 52, 54 have mounting portions 56 which are secured to the bottom side of top wall 28 by threaded fasteners 58 (FIG. 4). Member 60 extending between and integrally joined to brackets 52, 54 includes wall 62 engaging inclined surface 48 on portion 46 of top wall 28 and defining slot 64 with slot 30 through which paper 32 extends. Paper guide member 66 is spaced from roller 34 and has flange 57 secured to the bottom side of projection 46 of top wall 28 by threaded fasteners 68.

Member 60 also includes wall 70 closely spaced from the upper surface of roller 34 and having front edge 72 spaced from front edge 74 of paper guide member 66 to form opening 75 through which paper 32 extends from roller 34. Resilient pressure pad 76 is mounted on the upper surface of wall 70 with paper 32 extending thereover from opening 75. Wall 78 having papertearing edge 80 thereon has integral mounting brackets 82 at its opposite ends respectively mounted on brackets 52, 54. Paper 32 extends under wall 78 between brackets 82.

Roller shaft 50 has starwheel 84 and manual paper roll-up knob 86 secured to end 88 thereof, knob 86 having cylinderical portion 90 seated on curved portion 92 of end wall 24. Detent 94 mounted on wall 24 engages star wheel 84. Shaft 50 is mounted on brackets 52, 54 by means of a snap fit in grooves 55 (FIG. 4). Shaft 96 is retained so as to bias tension rollers 98 against roller 34 by spring clip members 99 formed from opposite sides of paper guide member 66 (FIG. 6).

Cylinderical guide rod 100 is mounted'on and extends between side walls 24, 26 of housing 22. Carriage 102 is slideably mounted on rod 100 for linear motion therealong, and is also pivotally mounted on rod 100 for transverse movement by pivoting thereon. Thermal printing head 104 comprises holder member 106 mounted on carriage 102 by threaded fasteners 108. Thermal printing matrix 110, which may be of the type described in the aforesaid Texas Instruments report, is mounted on the bottom surface 112 of member 106 in registry with pressure pad 76. Comparison of FIGS. 4

and 7 will show that carriage 102 and printing head 104 are pivotally movable on rod 100 between a printing position with matrix engaging strip 32 of thermally sensitive paper on pressure pad 76 (FIG. 4) and an inactive position with matrix 110 spaced from strip 32 and pressure pad 76 as shown in dashed lines at 104a in FIG. 4 and as shown in FIG. 7.

Referring now briefly to FIGS. 3A and 3B, carriage 102 and printing head 104 are linearly movable on rod 100 between right and left extreme positions 114, 116 through an intermediate, at-rest position 118 and an initial printing position 119. As will hereinafter be described, carriage 102 and printing head 104 are linearly moved in the direction shown by arrow 120 in incremental steps; in the illustrated embodiment, there are two such steps between the right hand end position 114 and the at-rest position 118, and I8 printing steps between the at-rest position 118 and the left hand end position 116. Carriage 102 and printing head 104 are pivoted on rod 100 to the printing position in all linear positions between the at-rest position 118 and the left hand end position 116, and are pivoted to the inactive position and all linear positions between the right hand end position 114 and the initial printing position 119.

Ramp 122 having cam surface 124 thereon is mounted on side wall 26 of housing 22 and cooperates printing head 104 being maintained in the inactive pov sition by engagement of projection 126 with high portion 130 (FIG. 7) of ramp 122-during continued movement in direction 128 to right hand end position 114 and return movement to at-rest position 118, as shown by arrow 130, as will hereafter be more fully described.

Carriage 102 and printing head 104 are linearlly moved on rod 100 by stepper motor 132 (FIGS. 4 and 8) having pinion 134 formed on its output shaft which drivingly engages toothed rack 136 on carriage 102. Pins 138 extending from motor mounting ring 140 are pivotally mounted in brackets 142, 144 suspended from top wall 28 of housing 22, stepper motor 132 thus being pivotally supported at or adjacent its balance point. Such pivotal mounting of stepper motor 132 accommodates the pivotal motion of carriage 102 caused by engagement of projection of 126 with ramp 122 and minimizes shock loading and changes in printing head pressure. Stepper motor 132 is biased so as pivotally to move carriage 102 and printing head 104 to the printing position by spring 146 having one end 148 engaging notch 150 in top wall 28 of housing 22 (FIG. 8 only) and its other end 152 engaging bracket 154 extending rearwardly from mounting ring 140. Thus, carriage 102 and printing head 104 are maintained in the printing position in all linear positions between the initial printi'ng position 119 (at which point projection 126 on carriage 102 moves off of cam surface 124 of ramp 122) and left hand end position 116 (FIG. 3B). It will be seen that spring 146 provides head pressure and wear take up, and also permits reasonable tolerances in manufacturing other parts of the apparatus and accommodates a lack of exact parallel relationship between rod 100 and roller 34.

Printed circuit board 156 is removably mounted in housing 22 adjacent its bottom edge 158 and carries the driving circuitry for the apparatus thereon. Flat,

multi-conductor flexible cable 160 couples printing edge 164 thereof to the respective mesas of matrix 110.

Flexible cable 160 has the same number of conductors therein which are bared adjacent its end 166. End 166 of said flexible cable 160 is disposed in overlapping relationship with end 164 of member 106 with the bared conductors of cable 160 in registry with and engaging conductors 162 on member 106, end 166 of cable 160 being retained in position'by being clamped between pad 170 and member 106 by threaded fasteners 108 (FIG. 7). It will be observed that flexible conductor 160 is disposed in a serpertine configuration between printing head 104 and printed circuit board 156 thereby to accommodate movement of carriage 102 and printing head 104.

Movement of carriage 102 in direction 128. from the at-rest position 118 to right hand end position 114 (FIG. 3) actuates rachet mechanism 172 to rotate roller 34 so as to advance strip 32 of thermally sensitive paper sufficiently to print another line of alphanumeric characters during the next operation of the apparatus. Referring more particularly to FIGS. 9 through 12 of the drawings, rachet mechanism 172 comprises rachet wheel 174 on shaft 50 and connected to roller 34. Carriage member 176 is rotatably mounted on shaft 50, carrier 176 and all other members mounted on shaft 50 being retained thereon by molded plastic washer 178, end 180 of shaft 50 being heat-staked into a chamfer in the bore of washer 178.

Carrier member 176 has pawl 182 mounted thereon by pin 184. Carrier member 176 has integral flange 186 formed thereon with annular slot 188 formed therein which defines leaf spring element 190 intergral with carrier 176. Leaf spring element 190 engages pawl 182 normally biasing it into driving engagement with rachet wheel 174. Pawl 182 has flange 192 thereon seated in slot 188 thereby to retain pawl 182 on pin 184.

Carrier 176 and pawl 182 are normally biased to the position shown in dashed lines in FIG. 11 by spring 194 having one end 196 engaging opening 198 in flange 56 on bracket 54, and its other end 200 engaging pin 202 on carrier 176. In the normal position of carrier 176, as shown in dashed lines in FIG. 11, pawl 182 engages abutment 204 on bracket 54 and is thereby biased out of engagement with rachet wheel 174 against the force exterted by leaf springelement 190.

. Bell crank lever 206 (FIGS. 2 and 9) is pivotally mounted on brackets 208, 210 extending from side wall 26 of housing 22. End 212 of bell crank lever 206 engages slot 214 in carrier member 176. Movement of carriage 102 in direction 128 to the at-rest position 118 (FIG. 3) causes abutment 216 on carriage 102 to engage the other end 218 of bell crank lever 206 (FIG. 9), and continued movement of carriage 102 from the atrest position 118 to the right hand end position 114 pivots bell crank lever 206 so that end 212 rotates carrier member 176 in the direction shown by arrow 220 from the position in dashed lines in FIG. 11 to the position shown in solid lines in FIGS. 10 and 11. This rotation of carrier member 176 in direction 220 moves pawl 182 out of engagement with abutment 204 so that leaf spring 190 biases pawl 182 into engagement with rachet wheel 174 thereby to rotate the same and roller 34 in direction 220 to advance strip 32 of thermally sensitive paper by one line. During return of carriage 102 from right hand end position 114 to at-rest postion 118, spring 194 returns carrier 176, pawl 182 and bell crank lever member 206 to the normal position, detent 94 in engagement with star wheel 84 preventing rota, tion of shaft and roller 34.

It will be observed that when carriage 102 and print ing head 104 are at the at-rest position 118, i.e., with carriage 102 and printing head 104 pivotally moved to the inactive position by engagement of projection 126 with ramp 122, but prior to actuation of rachet mechanism 172, strip 32 may be advanced or retarded by manual operation of roll-up knob 86.

Referring now briefly to FIG. 14, thermal printer apparatus 20 may be mounted in recess 224 in housing 226 of electronic calculator 228. It will be understood that roll 36 of thermally sensitive paper 32 may not be mounted on the rear of the thermal printer unit 20 as shown in the previous figures, but may be mounted in housing 226. Calculator 228 has a conventional keyboard 230 which does not form a part of the present invention.

. Referring now again to FIG. 3, in operation, carriage 102 and printing head 104 are initially at the at-rest or Zero position 118 with carriage 102 and thermal printhead 104 pivoted to the inactive position, as

I above-described. It will now be assumed that the operator has sequentially operated selected keyboard switches of keyboard 230 to enter a series of numbers comprising one line (up to eighteen in the illustrated embodiment) in the calculator memory. Upon actuation of a function switch, such as the +=s'witch 232, the interface circuitry causes stepping motor 132 to advance carriage 102 and printing head 104 one step in direction 120 to the initial or +1 printing position 119, this advance causing projection 126 on carriage 102 to ride down cam surface 124 on ramp ram 122 so that matrix engages paper 32 in +1 position 119. Upon the completion of the movement of carriage 102 and printing head 104 in direction by one incremental step to the +1 position 119, the interface and driving circuitry then energizes printing matrix 110 in accordance with the first character (number, letter or symbol) to be printed in the line causing that character to be printed on paper 32. Following printing of the first character in the line, the interface circuitry energizes motor 132 to advance carriage 102 and printing head 104 in direction 120 one incremental step to position +2 and following that one step advance, matrix 110 is energized to print the next character in the line, reading from right to left.

This sequential step advance-print operation continues until the interface circuitry detects that the last character has been read out and printed. The interface circuitry then energizes motor 132 to drive carriage 102 and printing head 104 in direction 128 thereby to return carriage 102 and printing head 104 to the right hand end position 114. As above described, movement of carriage 102 in direction 128 from the initial printing position 119 to the at-rest position 118 causes engagement of projection 126 with cam surface 124 on ramp 122 thereby to pivot carriage 102 and printing head 104 to the inactive position, carriage 102 and printing head 104 being maintained in the pivoted, inactive position during continued movement in direction 128 from the at-rest position 118 to right hand end position 114 by engagement of projection 126 on carriage 102 with high portion 130 of ramp 122. As above described, during movement in direction 128 from at-rest position 118 to right hand end position 114, rachet mechanism 172 is actuated to advance strip 32 of paper by one line.

Upon arrival of carriage 102 at right hand end position 114, end 234 of carriage 102 actuates limit switch 236. Actuation of limit switch 236 causes the interface and driving circuitry to reverse the energization of stepping motor 132 thereby to advance carriage 102 and printing head 104 in direction 130 by two steps from the right hand end position 114 to the at-rest position 118 at which point further advance of carriage 102 and printing head 104 is terminated awaiting entry of another line of characters, as above described.

Referring now to FIGS. and 16, a system is shown in block diagram form which may be employed for operating thermal printer apparatus from an electronic calculator. Calculator circuitry 238, which may be of the type more fully shown and described in application Ser. No. 256,286 now U.S.- Pat. No. 3,755,806 ofJames H. Bunting, assigned to the assignee of the present application, has binary-coded-decimal (BCD) output circuits 240 and functional output circuits 242 (in which signals appear in response to actuation of function switches) coupled to data interface timing and control circuitry 244. Circuitry 244 is coupled to character generator 246 which is coupled in turn to thermal print head driver circuitry 248 and thermal printing matrix 1 10.

Circuit 250 couples data interface timing and control circuitry 244 to mechanism interface timing and control circuitry 252 for applying stepper motor advance pulses thereto. Circuit 254 couples data interface timing and control circuitry 244 to mechanism interface timing and control circuitry 252 for applying a direction command signal thereto, such as a one level signal for causing the stepping motor 132 to advance carriage .102 and printing head 104 forwardly in direction 120 in response to advance pulses in circuit 250, and a zero level signal causing stepper motor 132 to return carriage 102 and printing head 104 in direction 120 to right hand end position 114. Circuit 256 couples mechanism interface timing and control circuitry 252 to data interface timing and control circuitry 244 to apply an at-rest position feedback signal thereto. Circuit 258 couples mechanism interface circuitry 252 to thermal printhead driver circuitry 248 to apply an enabling signal thereto to cause energization of thermal printing matrix 110 with the appropriate character following completion of the one step advance movement of carriage 102 and printhead 104. Mechanism interface timing and control circuitry 252 is coupled to mechanism driving circuitry 260, coupled in turn to printer mechanism 262 which, with thermal print matrix 110 comprises the thermal printing apparatus 20.

Referring additionally to FIG. 16, appearance of the zero" level signal in printer command circuit 254 couples pulse generator 264 to motor control circuitry 266 which forms a part of mechanism interface timing and control circuitry 252, pulse generator 264 generating a train of pulses for energizing stepper motor 132 to return carriage 102 and printing head 104 in direction 128 to right hand end position 114, as above described.

In accordance with one mode of operation of the interface and driving circuitry shown in FIGS. 15 and 16, calculator electronic circuitry 238 repetitively scans the characters entered in its memory registers thus repetitively providing, in sequential fashion, in its output circuits 240 coded data for the characters stored with coded data indicating the respective character, i.e., the

last character stored (the right hand character), next to last, et seq. Data interface timing and control circuit 244 includes counting circuitry which in essence interrogates the scanned coded data in calculator output circuitry 240 in inverse order of entry, i.e., upon actuation of a function switch, data interface timing and control circuitry 244 determines the last character entered which is to be printed in the right hand column on paper 32, applies 'the coded data for that character to character generator 246 which in essence is a code converter, character generator 246 converting thecoded data for the respective character to signals in the proper lines to energize the proper heating elements in thermal printing matrix so as to form the respective character.

As previously indicated, actuation of any function switch following entry of a line of numbers causes data interface timing and control circuitry 244 to apply a forward command signal in printer command circuit 254 and an advance pulse in circuit 250. Following a time delay sufficient to permit advance of carriage 102 and thermal printhead 104 by one step, a signal appears in enable circuit 258 which enables thermal printhead driver 248 to apply energizing signals from character generator 246 to thermal printing matrix 110. Data interface timing and control circuitry 244 maintains the energizing signals on thermal printing matrix 110 for a sufficient length of time to print the respective character at which point the energizing signals are'terminated and following a further short time delay to permit cooling of the heating elements, data interface circuitry 244 determines the coded data for the next-to-last number, another advance pulse is applied to mechanism interface timing and control circuitry 250, and character generator 246 generates signals appropriately to energize thermal printing matrix 110 thereby to print that character, as above-described.

Assuming now that four characters have been entered in the calculator memory, when data interface timing and control circuitry 244 interrogates the rapidly scanned coded data from the calculator memory for a fifth character, it will find that there is no such fifth character and will thus apply a zero" command signal in printer command circuit 254 thereby to reverse stepper motor 132 to return carriage 102 and printing head 104 to the right hand end position 114, as above-described. Closing ofcarriage limit switch 236 by carriage 102 when it reaches right hand end position 114 actuates the motor control 266 to energize stepper motor 132 for forward operation, two pulses provided by pulse generator 264 then causing advance of carriage 102 and printing head 104 by two steps to at-rest position 114 at which point a signal appears in at-rest position feedback circuit 256 which advises data interface timing and control circuitry 244 that the printing mechanism is now ready to print another line of characters.

Thermal printhead drive circuitry 248 may be printed on bottom side 112 of member 106 along with conductors 162, or may be provided on printed circuit board 156. The remaining circuitry shown in FIGS. and 16, other than calculator electronics 238, will be provided on printed circuit board 156 in conventional fashion.

It will be readily understood that the interface and driving circuitry shown in FIGS. 15 and 16 is illustrative only and that other interface and driving circuitry may be provided as dictated by the circuitry of the particular device with which thermal printing apparatus 120 is employed. It will also be understood that the characters to be printed need not be conventional Roman/Arabic in form.

It will be understood further that while a stepper motor 132 is shown and described, carriage 102 and printhead 104 may be moved linearly by other bidirectional actuator devicessuch as a solenoid or a motor with an intermittent motion mechanism such as a Geneva wheel. Further, while threaded fasteners 58, 68 are shown, the parts may be secured by other means such as heat-staked plastic pins.

it will now be seen that the construction of thermal printing apparatus 20 is characterized by its simplicity, relatively few number of parts many of which can be formed of molded plastic material, ease of assembly, and small size, FIGS. 2 and 4 being generally to full scale. It will further be seen that the apparatus of the invention will print any character (within the capability of the matrix) in any of its printing positions.

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

I. An apparatus for electrically recording successive lines of characters on a sheet of recording medium for visual display including a supporting frame, means mounted to said frame for holding said sheet in predetermined position to present a recording area upon which a line of characters are to be recorded, a recording head having .a plurality of recording elements thereon which upon engagement with said recording area and selective energization form a character and visually record the same on said recording area, and

' means for supporting said recording head with said elements facing said recording area: means for mounting said supporting means on said frame for linear movement laterally with respect to said recording area and between first and second spaced end positions, said mounting means also mounting said supporting means for movement between a recording position with said elements engaging said recording area and an inactive position with said elements spaced therfrom, means coupled between said frame and said supporting means for incrementally moving said supporting means on said mounting means between a plurality of discrete positions between said first and second end positions,

said discrete positions including in sequence said first end position, an intermediate at-rest position and an initial printing position, means coupled between said supporting means and said frame for moving said supporting means on said mounting means to said inactive position in response to linear movement of said supporting means by said incremental moving means from said initial recording position to said at-rest position in a direction toward said first end position and for maintaining said supporting means in said inactive position in all linear positions thereof between said at-rest position and said first end position, and means coupled between said frame and said supporting means for maintaining said supporting means in said recording position in all said discrete positions thereof between said initial recording position and said second end position.

2. The apparatus of claim 1 wherein said elements comprise a solid state thermal printer and said recording medium is thermally sensitive paper.

3. The apparatus of claim 1 further comprising control means for actuating said incremental moving means to advance said supporting means linearly in a direction toward said second end position in incremental steps, there being at least one of said steps between said first end position and said at-rest position, one step between said at-rest position and said initial recording position, and a plurality of said steps between said initial recording position and said second end position.

4. The apparatus of claim 2 further comprising means for generating a series of preselected groups of character signals, said control means including means for incrementally advancing said supporting means from said at-rest position toward said second end position, means for coupling said generating means to said elements to receive predetermined ones of said groups of character signals and to energize respective ones of said elements to form and record a character correspondingthereto, said control means including second means for actuating said linear moving means linearly to return said supporting means to said first end position in response to completion of a said series of groups of character signals and then to advance said supporting means to said at-rest position.

5. The apparatus of claim 1 wherein said mounting means is an elongated cylinderical rod having said supporting means slidably and pivotally mounted thereon thereby to provide said linear and second-named movements.

6. The apparatus of claim 1 wherein said incremental moving means comprises an elongated toothed rack on said supporting means, and power actuator means including a pinion drivingly engaging said rack for linearly moving the same and said supporting means.

7. The apparatus of claim 6 wherein said power actuator means isan electric motor.

8. The apparatus of claim 7 wherein said motor is a stepper motor.

9. The apparatus of claim 7 wherein said mounting means is an elongated member slidably and pivotally mounting said supporting means to provide said linear and second-named movements, said motor being pivotally mounted thereby to accommodate said pivotal movement of said supporting means.

10. The apparatus of claim 9 wherein said last-named maintaining means comprises a spring acting on said motor to urge the same to a position so that said pinion pivotally moves said rack and supporting means to said recording position.

11. The apparatus of claim 1 further comprising a frame, said second-named moving means including a cam surface on said frame and a cooperating cam follower on said supporting means.

12. The apparatus of claim 11 wherein said lastnamed maintaining means includes a spring.

13. The apparatus of claim 1 wherein said supporting means includes means operatively engaging said frame when said supporting means moves from said at-rest position to said first end position for advancing said sheet in response to movement of said supporting means from said at-rest position to said first end position thereby to present another recording area to said elements.

14. The apparatus of claim 13 wherein said holding means comprises a roller with said sheet passing partially therearound and means for holding said sheet in engagement with said roller, said advancing means comprising a ratchet wheel connected to said roller for rotating the same, a carrier member concentric with said ratchet and rotatable between first and second positions, said carrier member having a pawl pivotally mounted thereon, means on said carrier member for normally biasing said pawl into driving engagement with said ratchet wheel, means for normally urging said carrier member to said first position thereof, cam means for moving said pawl out of engagement with said ratchet wheel when said carrier member is in said first position thereof, and means for moving said carrier member to said second position thereof in response to said movement of said supporting means from said atrest position to said first end position thereby causing said pawl to engage said ratchet wheel and advance the same and said roller.

15. The apparatus of claim 14 wherein said lastnamed moving means comprises a bell crank lever ac- 17. The apparatus of claim 16 wherein said pawl is pivotally mounted on said carrier member by a pin, said spring being a leaf spring having a side edge spaced from said carrier member to define a slot, said pawl having a flange thereon which is received in said slot thereby retaining said pawl on said'pin.

I 18. The apparatus of claim 17 wherein said carrier member and leaf spring are integral.

19. The apparatus of claim 1 wherein said elements comprise a solid state thermal printer and said recording medium is an elongated strip of thermally sensitive paper, said frame having spaced side walls, said mounting means comprising an elongated cylindrical rod mounted on and extending between said sidewalls, said supporting means comprising a carriage member slidably and pivotally mounted on said rod thereby to provide said linear and second-named movements, said first moving means comprising a toothed rack on said said frame cooperatively engaging a part of said carriage in all linear positions thereof between said at-rest position and said first end position, said holding means comprising a roller on a shaft parallel with said rod with said strip passing partially therearound, and means for holding said strip in engagement with said roller, a ratchet wheel on said shaft and connected to said roller for rotating the same, a carrier member mounted on said shaft adjacent said ratchet wheel and rotatable between first and second positions, a pawl pivotally mounted on said carrier member, a spring acting between said carrier member and said pawl for normally biasing the same into engagement with said ratchet wheel, a spring acting between said frame and carrier member for normally biasing the same to said first position thereof, an abutment on said frame engaging said pawl in said first position of said carrier member and pivoting said pawl out of engagement with said ratchet wheel, a bell crank lever pivotally mounted on saidone end wall and having one end thereof engaging said carrier member, said bell crank lever having another end engaged by said carriage and moved thereby upon linear movement thereof from said at-rest position to said first end position so as to move said carrier member to said second position thereof thereby causing said pawl to engage said ratchet wheel and rotate the same and said roller to advance said strip to present another recording area to said elements.

20. The apparatus of claim 19 further comprising means for generating a series of preselected groups of character signals, control means for energizing said motor to step said carriage linearly and incrementally from said at-rest position toward said second end position at a predetermined stepping rate, means for coupling said generating means to said elements to energize respective ones thereof in response to completion of each said one step thereby to form and record a respective character, means for energizing said motor linearly to return said carriage to said first end position in response to completion of a said series of groups of character signals, means for sensing return of said carriage to said first end position, and means responsive to said sensing means for energizing said motor to advance said carriage from said first end position to said at-rest position in at least one incremental step, there being one incremental step between said at-rest position and said initial recording position. 

1. An apparatus for electrically recording successive lines of characters on a sheet of recording medium for visual display including a supporting frame, means mounted to said frame for holding said sheet in predetermined position to present a recording area upon which a line of characters are to be recorded, a recording head having a plurality of recording elements thereon which upon engagement with said recording area and selective energization form a character and visually record the same on said recording area, and means for supporting said recording head with said elements facing said recording area: means for mOunting said supporting means on said frame for linear movement laterally with respect to said recording area and between first and second spaced end positions, said mounting means also mounting said supporting means for movement between a recording position with said elements engaging said recording area and an inactive position with said elements spaced therfrom, means coupled between said frame and said supporting means for incrementally moving said supporting means on said mounting means between a plurality of discrete positions between said first and second end positions, said discrete positions including in sequence said first end position, an intermediate at-rest position and an initial printing position, means coupled between said supporting means and said frame for moving said supporting means on said mounting means to said inactive position in response to linear movement of said supporting means by said incremental moving means from said initial recording position to said at-rest position in a direction toward said first end position and for maintaining said supporting means in said inactive position in all linear positions thereof between said at-rest position and said first end position, and means coupled between said frame and said supporting means for maintaining said supporting means in said recording position in all said discrete positions thereof between said initial recording position and said second end position.
 2. The apparatus of claim 1 wherein said elements comprise a solid state thermal printer and said recording medium is thermally sensitive paper.
 3. The apparatus of claim 1 further comprising control means for actuating said incremental moving means to advance said supporting means linearly in a direction toward said second end position in incremental steps, there being at least one of said steps between said first end position and said at-rest position, one step between said at-rest position and said initial recording position, and a plurality of said steps between said initial recording position and said second end position.
 4. The apparatus of claim 2 further comprising means for generating a series of preselected groups of character signals, said control means including means for incrementally advancing said supporting means from said at-rest position toward said second end position, means for coupling said generating means to said elements to receive predetermined ones of said groups of character signals and to energize respective ones of said elements to form and record a character corresponding thereto, said control means including second means for actuating said linear moving means linearly to return said supporting means to said first end position in response to completion of a said series of groups of character signals and then to advance said supporting means to said at-rest position.
 5. The apparatus of claim 1 wherein said mounting means is an elongated cylinderical rod having said supporting means slidably and pivotally mounted thereon thereby to provide said linear and second-named movements.
 6. The apparatus of claim 1 wherein said incremental moving means comprises an elongated toothed rack on said supporting means, and power actuator means including a pinion drivingly engaging said rack for linearly moving the same and said supporting means.
 7. The apparatus of claim 6 wherein said power actuator means is an electric motor.
 8. The apparatus of claim 7 wherein said motor is a stepper motor.
 9. The apparatus of claim 7 wherein said mounting means is an elongated member slidably and pivotally mounting said supporting means to provide said linear and second-named movements, said motor being pivotally mounted thereby to accommodate said pivotal movement of said supporting means.
 10. The apparatus of claim 9 wherein said last-named maintaining means comprises a spring acting on said motor to urge the same to a position so that said pinion pivotally moves said rack and supporting means to said recording position.
 11. The apparatus of claim 1 further comprising a frame, said second-named moving means including a cam surface on said frame and a cooperating cam follower on said supporting means.
 12. The apparatus of claim 11 wherein said last-named maintaining means includes a spring.
 13. The apparatus of claim 1 wherein said supporting means includes means operatively engaging said frame when said supporting means moves from said at-rest position to said first end position for advancing said sheet in response to movement of said supporting means from said at-rest position to said first end position thereby to present another recording area to said elements.
 14. The apparatus of claim 13 wherein said holding means comprises a roller with said sheet passing partially therearound and means for holding said sheet in engagement with said roller, said advancing means comprising a ratchet wheel connected to said roller for rotating the same, a carrier member concentric with said ratchet and rotatable between first and second positions, said carrier member having a pawl pivotally mounted thereon, means on said carrier member for normally biasing said pawl into driving engagement with said ratchet wheel, means for normally urging said carrier member to said first position thereof, cam means for moving said pawl out of engagement with said ratchet wheel when said carrier member is in said first position thereof, and means for moving said carrier member to said second position thereof in response to said movement of said supporting means from said at-rest position to said first end position thereby causing said pawl to engage said ratchet wheel and advance the same and said roller.
 15. The apparatus of claim 14 wherein said last-named moving means comprises a bell crank lever actuated by said supporting means.
 16. The apparatus of claim 15 wherein said roller and ratchet wheel are mounted on a shaft, said carrier member being rotatably mounted on said shaft, said biasing means being a spring having one end connected to said carrier member and its other end engaging said pawl.
 17. The apparatus of claim 16 wherein said pawl is pivotally mounted on said carrier member by a pin, said spring being a leaf spring having a side edge spaced from said carrier member to define a slot, said pawl having a flange thereon which is received in said slot thereby retaining said pawl on said pin.
 18. The apparatus of claim 17 wherein said carrier member and leaf spring are integral.
 19. The apparatus of claim 1 wherein said elements comprise a solid state thermal printer and said recording medium is an elongated strip of thermally sensitive paper, said frame having spaced side walls, said mounting means comprising an elongated cylindrical rod mounted on and extending between said sidewalls, said supporting means comprising a carriage member slidably and pivotally mounted on said rod thereby to provide said linear and second-named movements, said first moving means comprising a toothed rack on said carriage, and an electric motor having a pinion on its shaft drivingly engaging said rack thereby linearly to move the same and said carriage, said motor being pivotally mounted on said frame therby to accommodate said pivotal movement of said carriage, said last-named maintaining means comprising a spring acting between said frame and said motor therby to urge the same to a position so that said pinion pivotally moves said rack and carriage to said recording position, said second-named moving means comprising a cam member on said frame cooperatively engaging a part of said carriage in all linear positions thereof between said at-rest position and said first end position, said holding means comprising a roller on a shaft parallel with said rod with said strip passing partially therearound, and means for holding said strip in engagement with said roller, a ratchet wheel on said shaft and connected to said roller for rotating the same, a carrier member mounted on said shaft adjaCent said ratchet wheel and rotatable between first and second positions, a pawl pivotally mounted on said carrier member, a spring acting between said carrier member and said pawl for normally biasing the same into engagement with said ratchet wheel, a spring acting between said frame and carrier member for normally biasing the same to said first position thereof, an abutment on said frame engaging said pawl in said first position of said carrier member and pivoting said pawl out of engagement with said ratchet wheel, a bell crank lever pivotally mounted on said one end wall and having one end thereof engaging said carrier member, said bell crank lever having another end engaged by said carriage and moved thereby upon linear movement thereof from said at-rest position to said first end position so as to move said carrier member to said second position thereof thereby causing said pawl to engage said ratchet wheel and rotate the same and said roller to advance said strip to present another recording area to said elements.
 20. The apparatus of claim 19 further comprising means for generating a series of preselected groups of character signals, control means for energizing said motor to step said carriage linearly and incrementally from said at-rest position toward said second end position at a predetermined stepping rate, means for coupling said generating means to said elements to energize respective ones thereof in response to completion of each said one step thereby to form and record a respective character, means for energizing said motor linearly to return said carriage to said first end position in response to completion of a said series of groups of character signals, means for sensing return of said carriage to said first end position, and means responsive to said sensing means for energizing said motor to advance said carriage from said first end position to said at-rest position in at least one incremental step, there being one incremental step between said at-rest position and said initial recording position. 